This invention relates to ground fault current interrupter and arc fault current interrupter circuit breakers and more particularly to such circuit breakers having a mechanism for opening the associated circuit in the event of a failure in the ground fault or arc fault trip circuit.
In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light industrial applications, overcurrent protection is typically provided by a thermal-magnetic trip device. This trip device typically includes a bimetal strip that is heated and bends in response to a persistent overload condition. The bimetal, in turn, unlatches a spring powered operating mechanism that opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
For short circuit protection, an armature, which is attracted by the sizable magnetic forces generated in a magnetic core by a short circuit, unlatches, or trips, the operating mechanism. As an example, the magnetic type actuation occurs when the hot line conductor becomes directly connected with ground or neutral, thereby bypassing the load. In many applications, a miniature circuit breaker may additionally provide ground fault and arc fault protection.
Ground fault current interrupter (GFCI) and arc fault current interrupter (AFCI) circuit breakers are well known in the art. Examples of ground fault and arc fault circuit breakers are disclosed in U.S. Pat. Nos. 4,081,852; 5,260,676; 5,293,522; 5,896,262; and 5,892,593. In ground fault circuit breakers, an electronic circuit typically detects leakage of current to ground and generates a ground fault trip signal. This trip signal energizes a trip solenoid, which unlatches the operating mechanism, often through deflection of the armature of the thermal-magnetic trip device.
Ground fault circuit breakers include both Class A (e.g., ground fault current of about 5 mA for people protection) and equipment protective devices (e.g., ground fault current of about 30 mA). A common type of ground fault detection circuit is the dormant oscillator detector including first and second sensor coils. The line and neutral conductors of the protected circuit pass through the first sensor coil. The output of this coil is applied through a coupling capacitor to an operational amplifier followed by a window comparator having two reference values. A line-to-ground fault causes the magnitude of the amplified signal to exceed the magnitude of the reference values and, thus, generates a trip signal. At least the neutral conductor of the protected circuit passes through the second sensor coil. A neutral-to-ground fault couples the two detector coils which causes the amplifier to oscillate, thereby resulting in the generation of the trip signal.
In conventional ground fault circuit breakers, the ground fault detection circuit is powered from the load side of the circuit breaker such that the ground fault detection circuit is not powered after the circuit breaker has detected a ground fault and, thus, has tripped. In this manner, the circuit breaker separable contacts are employed as a cut-off switch to remove power to the ground fault detection circuit and, thus, protect such detection circuit.
In the event of a failure in the electronic trip circuit, such as a component failure that disables the electronic trip circuit, the circuit breaker can remain energized after the failure. It is desirable to provide a fail-safe mechanism that would open the contacts of the breaker in the event of such failure. It is further desirable to provide a means for preventing resetting of the circuit breaker once the contacts have been opened as a result of such failure.
A circuit breaker includes a pair of separable contacts forming a pole, an operating mechanism for operating the electrical contacts, an electronic trip circuit responsive to currents flowing through the pole for operating the operating mechanism in response to predetermined conditions to open the separable contacts, and a mechanism for operating the operating mechanism in response to a failure in the electronic trip circuit. The mechanism may include a solenoid that is electrically connected to be energized in response to a failure in the electronic trip circuit and a linkage that operates the operating mechanism in response to operation of the solenoid.
When the electronic circuit breaker fails, voltage is transferred to an auxiliary solenoid, which will then activate the trip mechanism of the circuit breaker.
Circuit breakers constructed in accordance with this invention further include a mechanism for preventing resetting of the circuit breaker once the auxiliary solenoid has been activated. This disables the circuit breaker with the contacts in an open position.